The manufacture of commercial semiconductor devices is today largely a high-speed semi automated or automated operation. This invention is related to a particular step in the manufacturing process, namely the bonding of the electrical conductor leads to a substrate in which the semiconductor chip will be supported. The leads are used to connect the chip to outside circuitry.
It is a common practice in the machine assembly of semiconductor chips to convey the leads into the machine on an integral lead frame. The lead frame is normally a thin strip of the conductor metal which has been die stamped into a pattern comprising leads and supporting structure. The leads project from supporting structure and are aligned along the supporting structure in a spaced relationship that will place the free ends of the leads in proper position to be bonded to the substrate. The frame normally has positioning guides, such as apertures along the support frame, to facilitate the free ends of the leads being placed in the proper position above the substrate by aligning the apertures over a pin or pins of the machine.
The lead frames run through the machine as a continuous ribbon of frames during the step where bonding to the substrate occurs, the bonding machine, including the positioning guides locate the free ends of the leads above conductor pads on the substrate. With both the substrate and the leads in position, the bonding tool presses the free ends of the leads against the conductor pads of the substrate and effects a permanent bond by known means such as thermocompression or ultrasonic bonding. The frame and attached substrate then proceed through the remaining steps of the assembly machine, including wire bonding of the semiconductor chip on the substrate to the leads. One of the final steps in the process is a cutting step wherein the leads are cut free of the frame near the point where they are attached to the supporting structure. The leads are also bent to a proper angle, normally vertically downward at a point just outboard of the ceramic carrier.
It is important in the assembly process to maintain tolerances in the lead frame ribbon which will prevent a frame from becoming hung up in the machine at any stage. This invention is in particular concerned with maintaining the frame in a generally flat plane after the leads are bonded to a substrate such as a ceramic carrier and until the leads are cut away from the frame. The bonding process causes metal flow along the leads in a direction away from the bonding site. There may also be some thermal expansion along the lead from thermo compression bonding. Both of these phenomena will tend to increase the length of the lead. If uncompensated, this may result in the outer edges of the lead frame curling inward and vertically, (to the plane of the frame) in a shape similar to a potato chip. Moreover, the leads may themselves bend in a vertical curvature. Both of these results present problems for the processing machine.
It would be ideal to maintain the lead frame in a perfectly flat horizontal plane to keep close tolerances and proper positioning while passing through the machine. Thus, any device whereby the lengthening of the leads caused by bonding does not cause a curling or vertical deformation of the leads and lead frame is advantageous. This invention is related to such a device.